Duplexers (also referred to as a duplexer, an antenna duplexer, or a branching filter) are mainly used for wireless communication of mobile phones and the like. In recent years, as mobile phones and the like become to have high functionality, small and highly reliable components are demanded. To meet such a demand, there has been known a technique in which a chip component such as an acoustic wave filter is mounted on an upper surface of a wiring substrate by the flip chip method and is sealed by solder material as disclosed in Japanese Patent Application Publication No. 2006-203149 (Patent Document 1). In Patent Document 1, a metal layer is arranged in a circular pattern on an upper surface of a wiring substrate so as to fix a sealing solder on the wiring substrate. In a structure disclosed in Patent Document 1, a leakage electric field is generated from an acoustic wave filter due to the contact of a solder sealing portion with the acoustic wave filter. In order to suppress this leakage electric field, it has been known sandwiching an insulating layer having a permittivity lower than that of the acoustic wave filter between a chip component and a solder sealing portion as disclosed in Japanese Patent Application Publication No. 2010-74418 (Patent Document 2). It has been known to suppress the degradation of transmission-reception isolation characteristics by forming a duplexer including an acoustic wave filter by using a technique disclosed in Patent Document 2.
However, when further downsizing is performed in the duplexer in which the technique disclosed in Patent Document 1 and Patent Document 2 is used, an unnecessary signal leaks from a transmission side to a reception side through a circular metal layer formed on the upper surface of the wiring substrate, and transmission-reception isolation characteristics are degraded.